Differences between AssemblyCatalog overloaded constructors

I've been using the AssemblyCatalog(string) constructor in my project without experiencing problems -- until the day I ran it on a German OS with a German VS installed (my MEF thing is part of a VSPackage).

On that day, MEF loaded one (1) type instead of the expected three (3). After much fiddling about I finally tried the AssemblyCatalog(Assebly) constructor instead:

Thanks for responding; good to know there's a difference at least. Possibly one that belongs in the remarks of the API docs -- load context issues are tricky and not exactly mainstream.

Anyways, I have one or two experiments I want to try; I'll post anything interesting here. (I'd understand a total failure better than a partial failure at this point, so I'll persue this for a bit even though the problem is "solved" for the moment. As long
as it's not understood, it's not solved.)